This invention relates to a microelectromechanical systems (MEMS) switch device, and its method of manufacture. More particularly, this invention relates to a MEMS electrostatic plate switch, which is manufactured on two separate substrates.
Microelectromechanical systems are devices often having moveable components which are manufactured using lithographic fabrication processes developed for producing semiconductor electronic devices. Because the manufacturing processes are lithographic, MEMS devices may be made in very small sizes, and in large quantities. MEMS techniques have been used to manufacture a wide variety of sensors and actuators, such as accelerometers and electrostatic cantilevers.
MEMS techniques have also been used to manufacture electrical relays or switches of small size, generally using an electrostatic actuation means to activate the switch. MEMS devices often make use of silicon-on-insulator (SOI) wafers, which are a relatively thick silicon “handle” wafer with a thin silicon dioxide insulating layer, followed by a relatively thin silicon “device” layer. In the MEMS devices, a thin cantilevered beam of silicon may be etched into the silicon device layer, and a cavity is created adjacent to the thin beam, typically by etching the thin silicon dioxide layer below it to allow for the electrostatic deflection of the beam. Electrodes provided above or below the beam may provide the voltage potential which produces the attractive (or repulsive) force to the cantilevered beam, causing it to deflect within the cavity.
One known embodiment of such an electrostatic relay is disclosed in U.S. Pat. No. 6,486,425 to Seki. The electrostatic relay described in this patent includes a fixed substrate having a fixed terminal on its upper surface and a moveable substrate having a moveable terminal on its lower surface. Upon applying a voltage between the moveable electrode and the fixed electrode, the moveable substrate is attracted to the fixed substrate such that an electrode provided on the moveable substrate contacts another electrode provided on the fixed substrate to close the microrelay.
However, to fabricate the microrelay described in U.S. Pat. No. 6,486,425, the upper substrate must be moveable, so that the upper substrate must be thin enough such that the electrostatic force may cause it to deflect. The moveable substrate is formed from a silicon-on-insulator (SOI) wafer, wherein the moveable feature is formed in the silicon device layer, and the SOI wafer is then adhered to the fixed substrate. The silicon handle wafer and silicon dioxide insulating layer are then removed from the SOI wafer, leaving only the thin silicon device layer which forms the moveable structure.